1. Field of the Invention
The present invention relates to the reversible sealing of porous, oil bearing rock formations. More especially, this invention relates to a process for the temporary, either total or partial sealing of such formations, utilizing certain silicates, and which is useful in a variety of drilling operations, the reconditioning of wells and the treatment of wells during production.
2. Description of the Prior Art
The use of sealing agents to reduce or eliminate the permeability of subterranean formations in the treatment of oil wells is well known to this art. Permanent or temporary sealing methods are used in drilling operations, well reconditioning, completion, stimulation and tertiary recovery. Such fluids, the use of which necessitates temporary and reversible sealing, have been described, for example, in U.S. Pat. Nos. 3,516,496 and 4,369,843. According to these processes, sealing is obtained by means of organic polymer solutions. In another process, described in U.S. Pat. No. 4,018,286, supersaturated, high density saline solutions are used. The temporary sealing processes of the prior art have the disadvantage of being uncertain in relation to their temperature behavior and their longevity, and the destruction of the polymer gel is often difficult to control and this gives rise to residual permeabilities that are lower than the initial permeabilities.
The use of silicates in the petroleum industry is also known. Silicates are used as additives to cement mixtures or resins to plug large lost circulation zones during drilling or to prevent communication between several layers of the deposit during the cementing of casings. Silicates are also used in fracturation in order to obtain viscous gels having thixotropic properties. In these operations the silicates are used essentially alone as the appropriate additives, without a gelling additive. In the form of gels, the silicates are used in tertiary recovery operations for the plugging of high permeability zones to prevent excessive water intrusion into producing wells. Generally, the silicate gels heretofore used in the oil industry were intended to form permanent seals.